Want to build an immutable image, but how?

Hey all,

Oldtimer here. Been using Linux since Suse 8 (pre Zypper). I'm currently running Kubuntu 26.04 on my gaming PC and a laptop full time. I mostly live within my user context by using flatpak rather than snap, but I find myself having to install things by way of snap which requires root credentials / group access. I prefer to live within my user context exclusively as one would with SteamOS.

I'd like to build an immutable version of Kubuntu but I don't know where to start. How would one go about creating the "gold image" and then how would I go about updating that image?

I see that someone / a small team has done this with Fedora. The fork / distro is Bazzite.

Coming to you all because I'm trying not to feed the AI industry. Hoping to get some valuable feedback even if that points me to an article.

Edit: Thanks for the replies everyone. I want to have access to install things via Flatpak which only requires user level access. It doesn't have to be Kubuntu specifically, but I would like something debian based. Debian based had always felt the most stable to me, but I'm open to trying something new.

https://redd.it/1ummzxb
@r_linux